Topspin pace model, beatable CPU, boy run cycle, umpire reverb, z-order fix

- fake topspin: quality shots dive under extra effective gravity, so real pace
  (up to 28 m/s) can clear the net AND land in — without it the net-clearance
  loop silently slowed every shot to a coverable lob, which is why the CPU
  returned everything regardless of aim
- no grass-scraping: balls below ankle height (0.24m) are past you, both sides
- CPU: 0.45s shot-read delay, 4.3 m/s legs, half-speed recovery between shots.
  Verified gradient: perfect/good corner shots are winners, center balls and
  weak shots still come back
- player aimed shots go wider (3.3m vs 2.7m)
- ball boy: nano-banana mirrored stride frames (was stride-vs-hop), height
  1.2m, z-ordered against umpire and CPU (no more running over the chair)
- umpire voice through a synthesized convolver reverb — center-court PA echo

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

game.js

@@ -8,16 +8,18 @@
 const TUNE = {
   camZ: 36, camY: 9, camF: 280, horizon: 40,
   gravity: 9.2,            // slightly floaty vs 9.8 for readability
+  spinFactor: 0.9,         // extra dive on quality shots (fake topspin)
   bounceY: 0.58, bounceXZ: 0.78,
-  playerSpeed: 5.4, aiSpeed: 5.0,
+  playerSpeed: 5.4, aiSpeed: 4.3,
   reach: 1.3, aiReach: 1.6, // tight contact radius: the assist positions you, the tap must be honest
   swingWindup: 0.06,       // s before contact window opens
   swingWindow: 0.16,       // s contact window length
-  baseShotSpeed: 15, qualityShotSpeed: 9,   // horizontal m/s = base + q*quality
+  baseShotSpeed: 16, qualityShotSpeed: 12,  // horizontal m/s = base + q*quality; perfect timing = real pace
   serveSpeed: 21, serveQualitySpeed: 7,
   aimError: 2.4,           // m of scatter at quality 0
   perfectMs: 45,           // |offset from window center| for PERFECT
-  aiQualityMin: 0.55, aiQualityMax: 0.95, aiFlub: 0.05,
+  aiQualityMin: 0.45, aiQualityMax: 0.85, aiFlub: 0.09,
+  aiReaction: 0.45, // s before the CPU reads your shot — well-aimed corners are winners
   autoAssist: matchMedia('(pointer: coarse)').matches ? 1.15 : 0, // auto-run speed factor (mobile); slightly superhuman legs
 };
 
@@ -116,11 +118,25 @@ const audio = () => {
 // Umpire lines are pre-recorded files (assets/audio/*.m4a) played via WebAudio —
 // works on mobile where speechSynthesis is unreliable. say() remains the fallback.
 const VOICE = {};
+let reverbNode = null;
+function reverb(ac) { // stadium PA tail: exponentially decaying noise as impulse response
+  if (reverbNode) return reverbNode;
+  const len = ac.sampleRate * 1.3, ir = ac.createBuffer(2, len, ac.sampleRate);
+  for (let c = 0; c < 2; c++) {
+    const d = ir.getChannelData(c);
+    for (let i = 0; i < len; i++) d[i] = (Math.random() * 2 - 1) * Math.pow(1 - i / len, 2.8);
+  }
+  reverbNode = ac.createConvolver(); reverbNode.buffer = ir;
+  const wet = ac.createGain(); wet.gain.value = 0.35;
+  reverbNode.connect(wet).connect(ac.destination);
+  return reverbNode;
+}
 function voice(name, delay = 0) {
   const ac = audio();
   const play = buf => {
     const src = ac.createBufferSource(); src.buffer = buf;
-    src.connect(ac.destination); src.start(ac.currentTime + delay);
+    src.connect(ac.destination); src.connect(reverb(ac)); // dry + center-court echo
+    src.start(ac.currentTime + delay);
   };
   if (VOICE[name]) return play(VOICE[name]);
   fetch('assets/audio/' + name + '.m4a')
@@ -212,7 +228,7 @@ function sendBoy() {
   const dir = ball.x > 0 ? 1 : -1;        // enter from the opposite side so the pickup is mid-run
   boy = { x: dir > 0 ? -13 : 13, z: ball.z, dir, runT: 0 };
 }
-let aiServeT = 0, aiSwingCool = 0;
+let aiServeT = 0, aiSwingCool = 0, aiReactT = 9;
 const crowd = { cheer: 0, dots: [] };
 function buildCrowd() {
   crowd.dots.length = 0;
@@ -237,10 +253,10 @@ function setupPoint() {
 }
 
 // ------------------------------------------------------------- ballistics ----
-// Launch ball from (x0,y0,z0) so it lands at (tx, tz) with horizontal speed s. Returns velocity.
-function solveShot(x0, y0, z0, tx, tz, s) {
+// Launch ball from (x0,y0,z0) so it lands at (tx, tz) with horizontal speed s under gravity g.
+function solveShot(x0, y0, z0, tx, tz, s, g = TUNE.gravity) {
   const dx = tx - x0, dz = tz - z0, dist = Math.hypot(dx, dz), T = dist / s;
-  return { vx: dx / T, vz: dz / T, vy: (0.08 - y0 + 0.5 * TUNE.gravity * T * T) / T };
+  return { vx: dx / T, vz: dz / T, vy: (0.08 - y0 + 0.5 * g * T * T) / T };
 }
 
 function doHit(ch, quality, aim) {
@@ -250,26 +266,31 @@ function doHit(ch, quality, aim) {
   ball.x = ch.x + ch.facing * 0.5;
   ball.z = ch.z + (toFar ? -0.3 : 0.3);
   const err = () => (Math.random() * 2 - 1) * TUNE.aimError * (1 - quality);
-  let tx = aim.ax * 2.7 + err();
+  let tx = aim.ax * (ch.side === 'P' ? 3.3 : 2.7) + err(); // your aimed shots go properly wide
   let tzBase = aim.az < 0 ? 3.0 : aim.az > 0 ? 8.6 : 5.4;      // depth from target baseline
   let tz = (toFar ? tzBase : COURT.L - tzBase) + err() * 0.8;
   tx = Math.max(-5, Math.min(5, tx));
   let s = TUNE.baseShotSpeed + quality * TUNE.qualityShotSpeed;
-  let v = solveShot(ball.x, ball.y, ball.z, tx, tz, s);
+  // topspin: quality shots dive under extra effective gravity, which is what lets real
+  // pace arc over the net and still land in — the core tennis trade-off
+  const g = TUNE.gravity * (1 + quality * TUNE.spinFactor);
+  let v = solveShot(ball.x, ball.y, ball.z, tx, tz, s, g);
   // low contact → trade pace for loft until the net is cleared; good timing gets a
   // comfortable margin, sloppy timing keeps some tape risk
   const margin = 0.06 + 0.22 * quality;
   for (let i = 0; i < 8; i++) {
     const tN = (COURT.netZ - ball.z) / v.vz;
-    const yN = ball.y + v.vy * tN - 0.5 * TUNE.gravity * tN * tN;
+    const yN = ball.y + v.vy * tN - 0.5 * g * tN * tN;
     if (tN <= 0 || yN >= COURT.netH + margin) break;
-    s *= 0.9; v = solveShot(ball.x, ball.y, ball.z, tx, tz, s);
+    s *= 0.9; v = solveShot(ball.x, ball.y, ball.z, tx, tz, s, g);
   }
+  ball.g = g;
   ball.vx = v.vx; ball.vy = v.vy; ball.vz = v.vz;
   ball.lastHit = ch.side; ball.bounces = 0; ball.firstLand = null;
   if (ch.side === 'P') { // shot marker: where this will land — red means it's going out
     const ok = Math.abs(tx) <= COURT.W / 2 + 0.02 && tz >= -0.02 && tz <= COURT.netZ;
     outMarker = { x: tx, z: tz, out: !ok, t: 1.3 };
+    aiReactT = 0; // CPU hasn't read the shot yet
   }
   pock(0.9, 950);
   if (quality > 0.999) { hitstop = 0.05; flash = { text: 'PERFECT', t: 0.7 }; pock(0.5, 1600); }
@@ -280,7 +301,7 @@ function doHit(ch, quality, aim) {
 function tossBall(sv) {
   ball.active = true; ball.bounces = 0; ball.firstLand = null; ball.collected = false;
   ball.x = sv.x + 0.35 * (sv.side === 'P' ? 1 : -1); ball.z = sv.z; ball.y = 1.8;
-  ball.vx = 0; ball.vz = 0; ball.vy = 4.6;
+  ball.vx = 0; ball.vz = 0; ball.vy = 4.6; ball.g = TUNE.gravity;
   phase = 'toss';
 }
 function serveApexY() { return 1.8 + 4.6 * 4.6 / (2 * TUNE.gravity); } // ~2.95
@@ -291,7 +312,9 @@ function hitServe(sv, quality) {
   const boxZ = toFar ? COURT.svcFar + 1.6 : COURT.svcNear - 1.6;
   const s = TUNE.serveSpeed + quality * TUNE.serveQualitySpeed;
   const tzs = boxZ + (Math.random() * 2 - 1) * (1 - quality) * 1.5;
-  const v = solveShot(ball.x, ball.y, ball.z, boxX, tzs, s);
+  const g = TUNE.gravity * (1 + quality * 0.35); // kick serves dip a little too
+  const v = solveShot(ball.x, ball.y, ball.z, boxX, tzs, s, g);
+  ball.g = g;
   ball.vx = v.vx; ball.vy = v.vy; ball.vz = v.vz;
   ball.lastHit = sv.side; ball.bounces = 0;
   if (sv.side === 'P') outMarker = { x: boxX, z: tzs, out: !inServeBox(boxX, tzs), t: 1.3 };
@@ -374,7 +397,7 @@ function intercept(side) {
   const ch = side === 'O' ? O : P;
   const spd = side === 'O' ? TUNE.aiSpeed : TUNE.playerSpeed * TUNE.autoAssist;
   let { x, y, z, vx, vy, vz } = ball;
-  const g = TUNE.gravity, dt = 0.01;
+  const g = ball.g || TUNE.gravity, dt = 0.01;
   const inZone = side === 'O' ? zz => zz <= 9.5 : zz => zz >= COURT.L - 9.5;
   const home = side === 'O' ? { x: 0, z: 2.5 } : { x: 0, z: 22.8 };
   let fallback = null, deepest = null;
@@ -401,6 +424,7 @@ function trySwing(ch, isAI) {
   if (ball.lastHit === ch.side) return;
   const dx = ball.x - ch.x, dz = ball.z - ch.z;
   if (Math.hypot(dx, dz * 0.8) > reach || ball.y > 2.3) return;
+  if (ball.y < 0.24) return; // below the ankles the ball is past you — no grass-scraping saves
   // quality: how centered in the window the contact lands
   const center = TUNE.swingWindup + TUNE.swingWindow / 2;
   const off = Math.abs(t - center) / (TUNE.swingWindow / 2);
@@ -486,19 +510,21 @@ function update(dt) {
     if (ball.vy < 0 && ball.y < serveApexY() - 0.1) { phaseWasServe = true; hitServe(O, 0.6 + Math.random() * 0.35); }
   }
   if (phase === 'rally') {
-    const incoming = ball.active && ball.lastHit === 'P';
+    aiReactT += dt;
+    const incoming = ball.active && ball.lastHit === 'P' && aiReactT >= TUNE.aiReaction;
     const tgt = incoming ? intercept('O') : { x: 0, z: 2.5 };
+    const spd = TUNE.aiSpeed * (incoming ? 1 : 0.5); // slow recovery: wrong-footing wins points
     const dx = tgt.x - O.x, dz = tgt.z - O.z, d = Math.hypot(dx, dz);
     if (d > 0.1) {
-      O.x += dx / d * Math.min(TUNE.aiSpeed * dt, d);
-      O.z += dz / d * Math.min(TUNE.aiSpeed * dt, d);
+      O.x += dx / d * Math.min(spd * dt, d);
+      O.z += dz / d * Math.min(spd * dt, d);
       O.pose = O.pose === 'swing' ? 'swing' : 'run'; O.runT += dt;
       if (Math.abs(dx) > 0.25) O.facing = dx > 0 ? 1 : -1;
     } else if (O.pose === 'run') O.pose = 'idle';
     aiSwingCool -= dt;
     if (incoming && aiSwingCool <= 0 && O.swingT < 0) {
       // same radius trySwing uses for contact, so an armed swing actually connects
-      const near = Math.hypot(ball.x - O.x, (ball.z - O.z) * 0.8) < TUNE.aiReach && ball.y < 2.3 && ball.vz < 0;
+      const near = Math.hypot(ball.x - O.x, (ball.z - O.z) * 0.8) < TUNE.aiReach && ball.y < 2.3 && ball.y > 0.24 && ball.vz < 0;
       if (near) {
         if (Math.random() < TUNE.aiFlub) aiSwingCool = 0.5; // whiff: hesitates and misses
         else { O.swingT = TUNE.swingWindup + TUNE.swingWindow / 2; trySwing(O, true); O.swingT = -1; aiSwingCool = ball.lastHit === 'O' ? 0.4 : 0.12; }
@@ -509,7 +535,7 @@ function update(dt) {
 
   // --- ball physics
   if (ball.active) {
-    ball.vy -= TUNE.gravity * dt;
+    ball.vy -= (ball.g || TUNE.gravity) * dt;
     const oldZ = ball.z;
     ball.x += ball.vx * dt; ball.y += ball.vy * dt; ball.z += ball.vz * dt;
     // net: plane at netZ, only during rally flight
@@ -554,7 +580,7 @@ function update(dt) {
 
 function predictLanding() { // first-bounce point of the ball's current trajectory
   let { x, y, z, vx, vy, vz } = ball;
-  const g = TUNE.gravity, dt = 0.01;
+  const g = ball.g || TUNE.gravity, dt = 0.01;
   for (let i = 0; i < 300; i++) {
     vy -= g * dt; x += vx * dt; y += vy * dt; z += vz * dt;
     if (y <= 0) return { x, z };
@@ -586,7 +612,7 @@ function drawStatic(name, x, z, hMeters, bob = 0) {
 function drawBoy(b) {
   const img = SPR[Math.floor(b.runT * 10) % 2 ? 'x_boyrun1' : 'x_boyrun2']; if (!img) return;
   const p = proj(b.x, 0, b.z);
-  const h = 1.35 * p.s, w = h * img.width / img.height;
+  const h = 1.2 * p.s, w = h * img.width / img.height;
   ctx.fillStyle = 'rgba(0,0,0,0.25)';
   ctx.beginPath(); ctx.ellipse(p.x, p.y, w * 0.3, Math.max(1, h * 0.04), 0, 0, 7); ctx.fill();
   ctx.save(); ctx.translate(p.x, p.y - (Math.floor(b.runT * 20) % 2));
@@ -689,10 +715,10 @@ function render() {
   }
   if (outMarker) drawRing(outMarker.x, outMarker.z, outMarker.out ? '#ff5050' : '#f8e048');
 
-  // court staff, then entities far→near, net between
-  drawStatic('x_ump', 7.1, COURT.netZ, 2.7);
-  if (boy && boy.z <= COURT.netZ) drawBoy(boy);
-  drawChar(O);
+  // far-side drawables in z order (far → near), then the net, then the near side
+  const farSide = [{ z: O.z, f: () => drawChar(O) }, { z: COURT.netZ - 0.01, f: () => drawStatic('x_ump', 7.1, COURT.netZ, 2.7) }];
+  if (boy && boy.z <= COURT.netZ) farSide.push({ z: boy.z, f: () => drawBoy(boy) });
+  farSide.sort((a, b) => a.z - b.z).forEach(d => d.f());
   // net
   const nl = proj(-COURT.netW / 2, 0, COURT.netZ), nr = proj(COURT.netW / 2, 0, COURT.netZ);
   const nlt = proj(-COURT.netW / 2, COURT.netH, COURT.netZ), nrt = proj(COURT.netW / 2, COURT.netH, COURT.netZ);